Multiphasic pump for rotating cryogenic machinery

ABSTRACT

A mixed phase pump for rapidly rotating cryogenic machinery is disclosed, preferably for installation to a superconducting generator rotor. The superconducting generator rotor includes an inner and outer rotor structure joined in a thermally insulated configuration not unlike that of a Dewar flask. The inner rotor contains a support cylinder for a refrigerant, typically helium, which when refrigerated to 3.5° Kelvin at one half a standard atmosphere under the normal rapid rotation of the axially aligned support cylinder, classifies itself into a two-phase liquid gas system. The phases include an outer cylindrical helium pool and an axially inward gaseous core separated by a cylindrical gas-liquid interface. During normal operation of the rapidly revolving rotor, a pump removes the gas for recooling to a liquid state by receiving the gas in the vicinity of the axis of the rotor at an inlet. During abnormal operation including stator short-circuit and rapid rotational vibrational acceleration and deceleration of the rotor, the normal cylindrical interface between the cylindrical helium pool and the vapor core is destroyed. The vapor core in the vicinity of the pump inlet becomes multiphasic and the pump inlet can induct/ingest quantities of liquid. Accordingly, a pump with the liquid gas classification volume located outwardly from the gas inlet to the pump is disclosed. This liquid trap volume in the pump assures that the outward passage of gas only from the pump occurs. Stability of the two-phase gas-liquid system as well as the prevention of thermal stressing of torque-transmitting members of the high speed rotating rotor is prevented.

This is a division of application Ser. No. 750,794, filed 12/15/76, nowU.S. Pat. No. 4,120,169.

This invention relates to a multiphasic cryogenic pump for high speedrotating machinery. More particularly, a pump compatible with asuper-cooled generator rotor is disclosed.

STATEMENT OF THE PROBLEM

Super-cooled windings in generator rotors are desirable. Specifically,by maintaining the windings of the rotor in a super-cooled state, anincrease in generator efficiency of as much as 1% can be realized.

Additionally, super-cooled rotors and generator stators can be built toa much smaller diametric dimension. This includes a reduction in weightof the overall generator. Moreover, where the rotor is constructed to asmaller diameter, there is a resultant reduction of the problemsencountered in high-speed rotating rotors.

Super-cooled rotors consist of two separate parts. Outermost there is adamper shield and damper shield support. This damper shield serves thedual purpose of being an outer thermal jacket of the super-cooled rotoras well as preventing back electromotive forces, both electrical andmechanical, from penetrating through to the superconducting coils.

Innermost there is an inner rotor structure including thesuperconducting windings or coils immersed within a helium refrigeratedannulus. This helium refrigerated annulus typically maintains thetemperature of the superconducting coils at 4.3° Kelvin or below so thatsuperconductivity takes place. Allowing for the desired temperaturedrop, the multiphasic system of the helium refrigerated annulus ismaintained with a liquid boiling point of 3.5° Kelvin in liquid heliumat a pressure of half a standard atmosphere.

When the rotor is on line, the helium bath undergoes rapid rotation.This classifies the multiphasic system in the inner core into an outercylindrical pool of liquid helium with an inner gaseous core. Theliquid-gas interface is cylindrical and symmetrical about the axis ofrotation of the generator rotor.

Such generators, however, must be designed not only for their normaloperational state, but also for the parametric extremes which they canexpect to encounter in abnormal operation. Such an extreme is ashort-circuit of the generator stator which produces tremendous changesin and on the rotor.

These changes include rapid angular accelerations imparted to the highspeed rotating rotor. These accelerations destroy the cylindrical liquidgas interface. If the helium gas evacuating pump ingests/inducts liquidat the inlet, several undesirable effects can and do occur.

First, the pressure in the helium multiphasic helium bath changes,typically by dropping. Thermal balance of the two phase system isdestroyed.

Secondly, the gaseous helium is normally communicated away from therotor in very carefully spaced helium conduits. These helium conduitsare spaced so that the "torque tubes" communicating power to the rapidlyrotating generator rotor are maintained with a precise thermal gradient.Since these torque tubes transmit power, rapid change of their thermalstate under a stress condition can cause thermal stressing and evenfailure of such torque tubes.

Where liquid helium carryover would occur to such torque-transmittingsections of a rotor, failure of the rotor at and near the torque tubescould occur. Consequently, liquid helium carryover is to be avoided.

Finally, it is necessary in such super-cooled generator rotors to assurethat after they have passed through a stress condition that theirdeparture from a normal operating state is minimized and that theirreturn to a normal operating state is made as rapidly as possible.

SUMMARY OF THE PRIOR ART

Prior art superconducting generator rotors have traditionally relied ona simple radially disposed pipe to pump gaseous helium away from therotor to the conduits that maintain the torque tube thermal gradient.The end of the pipe nearer the axis of rotation is in directcommunication with the gas in the rotor. The end farther from the axisis in direct communication with the torque tube conduits. A pumpingaction arises from the rotational motion imparted by the pipe to the gasin the pipe. Due to the familiar centrifugal force, this gas is flungoutward with the result that the pressure at the end of the pipe that isnearer the axis of rotation is reduced. Thus gas is continuously drawninto the nearer (rotor) end and expelled from the farther (torque tube)end.

However, if the liquid-gas interface in the rotor is upset, as would bethe case during any abnormal operation, liquid helium leaves the rotorand is pumped through to the torque tube conduits. The result is toupset the precisely maintained thermal gradient along the torque tube,thereby subjecting the torque tube to thermal stressing and an increasedrisk of failure.

SUMMARY OF THE INVENTION

A mixed phase pump for rapidly rotating cryogenic machinery isdisclosed, preferably for installation to a superconducting generatorrotor. The superconducting generator rotor includes an inner and outerrotor structure joined in a thermally insulated configuration not unlikethat of a Dewar flask. The inner rotor contains a support cylinder for arefrigerant, typically helium, which when refrigerated to 3.5° Kelvin atone half a standard atmosphere under the normal rapid rotation of theaxially aligned support cylinder, classifies itself into a two-phaseliquid gas system. The phases include an outer cylindrical helium pooland an axially inward gaseous core separated by a cylindrical gas-liquidinterface. During normal operation of the rapidly revolving rotor, apump removes the gas for recooling to a liquid state by receiving thegas in the vicinity of the axis of the rotor at an inlet. Duringabnormal operation including stator short-circuit and rapid rotationalvibrational acceleration and deceleration of the rotor, the normalcylindrical interface between the cylindrical helium pool and the vaporcore is destroyed. The vapor core in the vicinity of the pump inletbecomes multiphasic and the pump inlet can ingest or receive or inductquantities of liquid. Accordingly, a pump with the liquid-gasclassification volume located outwardly from the gas inlet to the pumpand a large flowing classification volume between inlet and outlet isdisclosed. This liquid trap volume in the pump assures that the outwardpassage of gas only from the pump occurs. Stability of the two-phasegas-liquid system as well as the prevention of thermal stressing oftorque-transmitting members of the high speed rotating rotor isprevented.

OTHER OBJECTS AND ADVANTAGES

An object of this invention is to disclose a rotor cryogenic pump forevacuating gas, which pump can be multiphasic in a rotor stresscondition. According to this aspect of the invention a pump is providedwith an inlet adjacent the rotor axis and an outlet adjacent the rotorperiphery. Between the inlet and outlet there is provided at least onedown-coming passageway which allows the centrifugal force of the rotorto pump gas from pump inlet to outlet. A liquid trap is provided at theperiphery of the pump radially outward from the pump outlet. Where thepump inlet sees a multiphasic condition, the pump serves to separate andtrap quantities of liquid which would otherwise destroy the thermalequilibrium of the rotor.

An advantage of the pump herein disclosed is that the pressure of atwo-phase system is maintained. The pump does not draw down thecylindrical volume pressure to destroy the design temperatures of thetwo-phase gas-liquid system.

A further advantage of this invention is that carryover of liquid totorque transmitting parts of the rotor is avoided. By avoiding suchliquid carryover, the thermal gradient in such torque transmitting partsis maintained substantially unchanged. Thermal stressing and evenfailure of generator torque tubes is avoided.

Yet another advantage of this invention is that a rapid return of therotor to a normal generator operating state is assured. Moreover, anydeparture of the rotor from a normal operating state during a stresscondition is kept to a minimum.

Other objects, features and advantages of this invention will becomemore apparent after referring to the following specification andattached drawings in which:

FIG. 1 is a perspective view of the helium flow circuit of asuper-cooled generator rotor;

FIG. 2 is a cross-section of the rotor adjacent the torque tubeillustrating the helium support center, helium pool, vapor core, andpump of this invention, the pump being shown in section;

FIG. 3 is a view partially in perspective illustrating one embodiment ofthe pump and its communication of gaseous helium to the torque tube ofthe generator rotor; and,

FIG. 4 is a sectional view of an alternate embodiment of the pump ofthis invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, the perspective view of the helium flow circuit ofthe super-cooled generator rotor is illustrated. Typically, helium istransferred to the rapidly rotating rotor through a rotating heliumtransfer system 14 such as that shown and described in the Institute ofElectrical and Electronic Engineers' Paper No. C 73-255-7 entitled"Development of a 5MVA Superconducting Generator, Mechanical andCryogenic Design", by T. J. Fagen et al. Helium flows along an inletpassage 16 coaxial with the rotor, which terminates in a conventional"T" feed tube 18. Tube 18 communicates interiorly of a helium managementsupport cylinder 20 (see FIG. 2), which cylinder is not shown in theschematic view of FIG. 1. Liquid helium communicated from transfersystem 14 through conduit 16 to "T" feed 18 forms a multiphasicliquid-gas two-phase system.

As can be seen in FIG. 2, a cylindrical liquid helium pool 22 is formedwith an inner gaseous helium core 24. Between the respective pool andgaseous core, there is located a cylindrical helium interface 23.

The interior of the rotor includes numerous heat exchangers. Thefunction of these heat exchangers is to communicate liquid helium at3.5° Kelvin under half an atmosphere of pressure in the vicinity of thegenerator windings 25. As the windings and heat exchangers do notconstitute the point of novelty of this invention, they will nothereinafter be described with particularity.

Once the helium cools the windings, the latent heat of evaporation takenfrom the windings causes the helium to become gaseous. This gas iscommunicated to gaseous core 24 of the two-phase system.

In core 24, gas typically outflows through pump A. It is classified inpump A and then passes through an outlet conduit 30 to a torque tubecoolant manifold 32.

It should be appreciated that pumps A₁ and A₂ are located at each end ofthe rotor. Pump A₁ and the manifold 32 (FIG. 1) communicated thereto tocool a torque-transmitting torque tube B (FIG. 2). The manifold 32discharges concentrically of the rotor in an outlet conduit 36 extendingthrough the gaseous core. Pump A₂ typically is located at the non-torquetransmitting tube communicated to the rotor. Its manifolds 32communicate to a helium outlet 37. Outlets 36 and 37 discharge torefrigerating machinery (not shown).

Having set forth the configuration flow of the helium, attention can nowbe devoted to the section of an actual rotor with respect to FIG. 2.

Referring to FIG. 2, a generator supported by rotating bearing not shownis illustrated in section between a torque tube B and a rotor section C.Torque tube B defines interiorly thereof a vacuum chamber 50 havingspaced helium gas outlets 32. Torque tube B immediately adjacent therotor C includes a pump blank 52. (See FIGS. 2 and 3.) Blank 52 haspaired helium inlets 55 and paired helium outlets 57. Typically, blank52 includes milled semi-arcuate walls 60 which define cavities 61 withineach of which is located a plurality of spaced radial vanes 62. Innormal operation, gaseous helium from core 24 flows through inlets 55.Once the gas is through inlets 55, the rotation of the rotor (commonlyrotating in the range of 3600 rpm) expells the gas outwardly undercentrifugal force. The gas, once expelled, passes through conduit 57 andthen into outlet 30 and the communicated torque tube manifolds 32.Torque tube manifolds 32 are precisely designed and spaced forpreserving a carefully chosen temperature gradient along the length ofthe torque tube. By maintaining this carefully chosen temperaturegradient, the torque tube has sufficient strength to support the weightof the inner rotor to withstand the forces of rapid rotation, and at thesame time to transmit the necessary torque for the rotor to rotate.

It is to be carefully noted that outlets 57 are spaced radially inwardfrom the radially outermost periphery of the cavity 61 (which peripherycorresponds, in the embodiment shown, to the periphery of the pump blank52 where it contacts the interior of the torque tube B). Thus a liquidhelium storage volume 65 is defined between the radially outermostperiphery of the cavity 61 and the outlet 57 of the pump.

Assuming that the rotor was being subject to the stress of themultiphasic condition previously described, and assuming that the liquidhelium interface 23 is broken down, some entry of liquid helium intoconduits 55 can be anticipated. In entering into conduits 55, liquidsegments of helium pass outwardly between the "downcoming" vanes. Insuch passage they fall outwardly to and are contained within the heliumstorage volume 65.

Helium outlet 57, nevertheless, will typically see a gaseous flow. Thisis because the liquid will be centrifugally classified out in the pumpblank 52 to the volume 65.

As it is normally expected that the generator stress condition will onlylast for a relatively short interval of time, the condition of liquidhelium outflow at inlet 55 will be relatively short lived. Accumulatedhelium within the liquid helium storage volume 65 will thereafter boiloff. It will pass outwardly of the pump blank at outlet 57 in thedesired gaseous state.

Referring to FIG. 4, an alternate embodiment of the pump blank 52a isshown. The pump blank includes an inlet 55 and an outlet 57.

Three paired spaces are each defined by drilling in the radiallyextending blank three apertures 81, 82 and 83. These apertures divergefrom each other at an approximate angle of 25° and intersect it at acommon communicating area 84 in the vicinity of inlet 55. Respectivepassageways 81, 83 are carried to a radial depth which exceeds the depthof central passageway 82. At the outer portion, the passageways arecommunicated by cross conduits 90, 91. These conduits are likewisedrilled. Typically, the open ends of the respective bores 81-83 aresealed as by welding of the blank.

In operation, the functioning of the pump blank 52a is precisely thesame; gaseous helium inflows from an inlet 55 and outflows through anoutlet 57. Liquid helium is accumulated in the storage space 86. Whensuch liquid helium boils off from the storage space 86, it outflowsthrough outlet 57 and the connected piping as heretofore described.

It should be appreciated that the pump according to FIG. 4 is easier tofabricate. For this reason, the pump blank of FIG. 4 is preferred.

What is claimed is:
 1. A superconducting generator rotor including atleast one torque tube for communicating torque to said rotor andsupporting the weight of said rotor; windings mounted to said rotor;means for supporting a multiphasic refrigerant system within theinterior of said rotor including a cylindrical chamber, an inlet forliquid refrigerant, said liquid refrigerant defining a pool at theperiphery of said cylindrical chamber, and an outlet for gaseousrefrigerant, said gaseous refrigerant defining a cylindrical corecoaxial with said cylindrical chamber, and a pump communicated to saidoutlet for extracting gaseous refrigerant, said pump including a pumphousing, said pump housing rotatable about an axis substantiallycoincident to the axis of said cylindrical chamber; said pump housingdefining at least one passageway extending from a first end adjacent theaxis of rotation of said pump housing to an opposite end radially remotefrom the axis of rotation of said pump housing; a gaseous helium inletcommunicated to said gaseous refrigerant core at one end and to saidaxially adjacent portion of said passageway at the opposite end toprovide for the inflow of gaseous refrigerant from said core to saidpump; a gaseous refrigerant outlet removed axially outward from saidinlet, said outlet communicating to said pump passageway at a distanceless than the full radially outward distance of said pasageway to permitthe outflow of helium gas from said pump; and, said passageway definingbetween said outlet and the axially remote portion of said passage aliquid refrigerant storage volume to prevent liquid that penetrates insaid inlet from gaining access to said pump outlet.
 2. In asuperconducting generator rotor including a support cylinder rotatedsubstantially about its axis containing a two-phase liquid-gasrefrigerant wherein said liquid is normally classified to the radialperiphery of said support cylinder to define a cylindrical pool and saidgas classified to the radial interior of the refrigerant to define agaseous refrigerant core with a cylindrical liquid gas interfacetherebetween, said rotor also including a torque tube for communicatingtorque to said rotor; said torque tube containing thereupon torque tubeconduits in fluid communication with said support cylinder; said rotoralso including means for withdrawing gaseous refrigerant from withinsaid support cylinder and communicating the gaseous refrigerant thuswithdrawn to said torque tube conduits including a radially extendingconduit having radially inward portion for receiving gas and liquidcarryover and a radially outward portion for discharging gas, thecombination with said means of withdrawing gaseous refrigerant, meansfor preventing liquid refrigerant from being communicated to said torquetube conduits including a liquid refrigerant storage volume radiallyoutward of said conduit and communicated to said radially outwardportion of means of withdrawing gaseous refrigerant to retain liquidcarry over from gaseous outflow from said refrigerant core.
 3. Theinvention in claim 2 and wherein said means for withdrawing gaseousrefrigerant and said means for preventing liquid refrigerant from beingcommunicated to said torque tube conduits together are embodied in apump comprising: a pump housing, said pump housing rotatable about anaxis substantially coincident to the axis of said refrigerant supportcylinder; said pump housing defining at least one passageway extendingfrom a first end adjacent the axis of rotation of said pump housing toan opposite end radially remote from the axis of rotation of said pumphousing; a gaseous helium inlet communiated to said gaseous refrigerantcore at one end and to said axially adjacent portion of said passagewayat the opposite end to provide for the inflow of gaseous refrigerantfrom said core to said pump; a gaseous refrigerant outlet removedaxially outward from said inlet, said outlet communicating to said pumppassageway at a distance less than the full radially outward distance ofsaid passageway to permit the outflow of helium gas from said pump; and,said passageway defining between said outlet and the axially remoteportion of said passage a liquid refrigerant storage volume to preventliquid that penetrates in said inlet from gaining access to said pumpoutlet.